This invention relates to helically corrugated, flexible tubing, especially rubber tubing of the type disclosed in U.S. Pat. No. 2,832,096. More particularly, the invention relates to a method for making such flexible, corrugated tubing and especially to a novel variation of the method of U.S. Pat. No. 2,832,096 of Vance M. Kramer et al, sometimes referred to as the "cording" method.
As disclosed in U.S. Pat. No. 2,832,096, helically corrugated tubing may be made by first drawing an extruded sleeve of uncured rubber axially over an elongated, rotatable mandrel with a core strip wrapped around it to form a single, continuous, external thread. The uncured rubber sleeve is forced into the helical groove or root of the thread by a length of cord wrapped around the sleeve to impart a desired corrugated shape. The rubber sleeve is cured in this condition and the cord removed. After curing, the resulting hose length may be removed from the mandrel and the core strip in a number of ways, such as by being blown off by air pressure between the mandrel and the cured tube, as described in U.S. Pat. No. 2,888,712.
The resulting helically corrugated hose length is both flexible and strong, yet still maintains its tubular form in a semi-rigid condition. This type of hose has particular application for use in domestic and industrial vacuum cleaners, as engine exhaust tubing, or tubing for ventilation systems, as well as in other appropriate applications.
In practice, tube lengths of many different diameters are made to satisfy market demand, and in the past it has been necessary to have a mandrel of a specific size for each of the various sizes of tube to be manufactured. Because of the time required in the "cording" and "uncording" steps of the process, considerable time is utilized in forming the extruded sleeve before curing, and in preparing the cured tube length for removal from the mandrel.
The method of the present invention, however, provides a novel variation on the basic "cording" process by which two tube lengths may be corded, cured, and and uncorded at the same time, thus eliminating entirely the "cording," "curing," and "uncording" process for one of the two tube lengths being manufactured.